UNIVERSITY  OF   CALIFORNIA  PUBLICATIONS 


COLLEGE  OF  AGRICULTURE 

AGRICULTURAL  EXPERIMENT  STATION 

BERKELEY,  CALIFORNIA 


THE   AVOCADO   IN   CALIFORNIA 

PART  I. -CULTURE,   PRODUCTION,  AND  MARKETING 

BY 
IRA  J.  CONDIT 

PART  II.-COMPOSITION   AND   FOOD   VALUE 

BY 
M.  E.  JAFFA 


BULLETIN  No.  254 

Berkeley,  Cal.,  May,  1915 


UNIVERSITY  OF  CALIFORNIA  PRESS 

BERKELEY 

1915 


Benjamin  Ide  Wheeler,  President  of  the  University. 

EXPERIMENT  STATION  STAFF 

HEADS  OP  DIVISIONS 

Thomas  Forsyth  Hunt,  Director. 

Eugene  W.  Hilgard,  Agricultural  Chemistry  (Emeritus). 

Edward  J.  Wickson,  Horticulture. 

Herbert  J.  Webber,  Director  Citrus  Experiment  Station;  Plant  Breeding. 

Hubert  E.  Van  Norman,  Vice-Director;  Dairy  Management. 

William  A.  Setchell,  Botany. 

Myer  E.  Jaffa,  Nutrition. 

Robert  H.  Loughridge,  Soil  Chemistry  and  Physics  (Emeritus). 

Charles  W.  Woodworth,  Entomology. 

Ralph  E.  Smith,  Plant  Pathology. 

J.  Eliot  Coit,  Citriculture. 

John  W.  Gilmore,  Agronomy. 

Charles  F.  Shaw,  Soil  Technology. 

John  W.  Gregg,  Landscape  Gardening  and  Floriculture. 

Frederic  T.  Bioletti,  Viticulture  and  Enology. 

Warren  T.  Clarke,  Agricultural  Extension. 

John  S.  Burd,  Agricultural  Chemistry. 

Charles  B.  Lipman,  Soil  Chemistry  and  Bacteriology. 

Clarence  M.  Haring,  Veterinary  Science  and  Bacteriology. 

Ernest  B.  Babcock,  Genetics. 

Gordon  H.  True,  Animal  Husbandry. 

James  T.  Barrett,  Plant  Pathology. 

Fritz  W.  Woll,  Animal  Nutrition. 

A.  V.  Stubenrauch,  Pomology. 

Walter  Mulford,  Forestry. 

W.  P.  Kelley,  Agricultural  Chemistry. 

William  G.  Hummel,  Agricultural  Extension. 

Leon  M.  Davis,  Dairy  Industry. 

John  E.  Dougherty,  Poultry  Husbandry. 

Frank  Adams,  Irrigation  Practice. 

David  N.  Morgan,  Assistant  to  the  Director. 

Mrs.  D.  L.  Bunnell,  Librarian. 

Division  of  Citriculture 
J.  Eliot  Coit  Ira  J.  Condit 

Division  of  Nutrition 
Miss  J.  E.  Davis  M.  E.  Jaffa 

Mrs.  A.  F.  Morgan  E.  J.  Lea 

Miss  M.  E.  Stover 


AVOCADO  CULTURE  IN  CALIFORNIA 


BY 
IRA  J.  CONDTT 


The  avocado  is  a  fruit  native  to  the  tropical  and  semi-tropical 
regions  of  North  and  South  America,  where  it  is  used  as  a  common 
and  much-prized  article  of  food.  From  its  native  home  it  has  spread 
to  practically  all  tropical  countries.  Since  its  introduction  into  Cali- 
fornia, at  Santa  Barbara  in  1870,  many  trees  grown  from  seed  obtained 
from  Mexico,  Guatemala,  Hawaii,  and  from  local  trees,  have  been 
planted,  principally  in  the  southern  part  of  the  state.  The  abundant 
fruiting  of  many  of  these  seedling  trees  and  the  high  prices  received 
for  the  fruit  in  local  markets  account  for  the  rather  sudden  interest 
in  avocado  planting.  Many  orchards  ranging  in  size  from  a  fraction 
of  an  acre  to  five  or  ten  acres  have  been  planted  in  various  sections 
of  the  state  and  much  larger  plantings  are  contemplated. 

The  avocado  tree  is  an  evergreen  with  fairly  large,  leathery  leaves 
and  under  favorable  circumstances  reaches  a  height  of  sixty  or  even 
eighty  feet.  It  belongs  to  the  Laurel  family,  the  leaves  having  the 
spicy  odor  and  taste  common  to  plants  of  this  family.  This  odor  is 
usually  much  more  noticeable  in  the  leaves  of  the  hardy  thin-skinned 
Mexican  varieties  than  in  the  more  tropical  hard-shelled  varieties. 
The  fruit  varies  in  form  from  round  to  pear-shaped  with  a  short  or 
elongated  neck,  and  in  weight  from  a  few  ounces  to  four  or  five  pounds. 
It  contains  a  single  large  seed  which  is  surrounded  by  yellowish, 
buttery  flesh.  The  fleshy  edible  part  is  rich  in  protein  and  oil,  the 
percentage  of  the  latter  varying  from  9.8  to  29.10  per  cent.  (See  p.  400.) 
The  flavor  and  quality  are  also  extremely  variable ;  undoubtedly  some 
varieties  which  are  excellent  so  far  as  early  bearing  and  productiveness 
of  tree  and  size  and  shape  of  fruit  are  concerned  will  have  to  take 
lower  rank  on  account  of  poor  quality. 

The  flesh  of  the  avocado  is  essentially  a  vegetable  butter,  a  sub: 
stantial  food.  The  fruit  contains  an  extremely  small  amount  of  acid 
and  sugar  and  a  very  large  amount  of  oil,  but  on  account  of  its 
scarcity  has  been  used  in  the  United  States  almost  entirely  as  a  salad, 
requiring  only  a  little  salt  and  lemon  juice  or  vinegar  to  make  it 

[381] 


382 


UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 


Fig.  1. — The  Taft  avocado  averages  over  one  pound  in  weight.  The 
tree  blossoms  in  the  spring,  the  fruit  maturing  in  about  fifteen  months, 
although  it  may  be  held  on  the  tree  three  or  four  months  longer. 


Bulletin  254  THE  AV0CAD0  IN  CALIFORNIA  383 

acceptable  to  most  palates.  In  fact,  from  the  earliest  records  up  to 
the  present  time  the  flesh  of  the  avocado  has  been  described  as  a 
natural  mayonnaise  and  is  often  eaten  as  taken  from  the  fruit,  with- 
out additional  preparation.  The  natives  of  Mexico  spread  the  pulp 
on  their  black  bread  in  place  of  butter. 

The  rapid  growth  of  young  trees,  the  early  fruiting  and  prolific- 
ness  of  many  good  varieties,  the  high  food  value,  and  the  popular 
demand  for  the  fruit  have  caused  many  fruit-growers  to  become 
interested  in  the  commercial  possibilities  of  the  avocado  in  those  sec- 
tions of  the  state  where  climatic  conditions  are  most  favorable.  It 
is  hoped  that  the  information  herein  set  forth  may  prevent  some  of 
the  mistakes  which  are  likely  to  occur  in  the  development  of  any 
new  fruit  industry. 

CLIMATIC  REQUIREMENTS 

Many  types  of  avocados  have  been  introduced  into  California, 
some  from  the  tropical  lowlands  of  Hawaii,  Mexico,  and  Central 
America ;  others  from  the  highlands  of  Mexico,  where  the  winter 
frosts,  although  quite  severe,  do  not  entirely  prevent  the  production 
of  abundant  crops.  In  general,  the  thin-skinned  Mexican  varieties 
have  proved  hardier  than  the  hard-shelled  Guatemalan  types.  Hard- 
shelled  varieties  from  elevations  of  5000  to  6000  feet  in  Mexico,  Co- 
lumbia, and  Chili  have  already  been  introduced  and  it  is  believed  that 
they  will  prove  hardy  in  the  citrus-growing  districts  of  California. 
It  is  advisable,  however,  to  test  out  the  fruiting  qualities  of  these  new 
varieties  under  our  climatic  conditions  before  planting  them  exten- 
sively. Some  types  will  be  uninjured  by  ten  degrees  of  frost,  provided 
the  season's  growth  is  properly  hardened  by  reducing  the  amount  of 
water  during  the  latter  part  of  the  season ;  other  types  are  injured 
by  three  or  four  degrees  of  frost,  while  the  strictly  tropical  varieties 
will  not  withstand  even  cold,  frostless  nights,  the  leaves  and  tender 
branches  turning  brown  and  dying  back  under  such  conditions. 
Mature  trees  themselves  are  not  so  subject  to  damage  on  frosty  nights 
as  the  blossoms  and  young  fruit  of  winter-flowering  varieties.  Varie- 
ties of  the  Guatemalan  type  usually  bloom  so  late  in  the  spring  that 
there  is  very  little  danger  of  frost.  The  partly  matured  fruit  of  such 
varieties  usually  passes  through  the  winter  without  injury  except  in 
unusually  severe  seasons,  such  as  that  of  1912-13,  when  the  freezing 
of  the  stems  caused  the  fruits  to  drop.  It  is  advisable  to  protect 
young  trees  from  frost  during  the  first  two  or  three  seasons  with 
cornstalks,  palm  leaves,  burlap,  or  by  the  use  of  orchard  heaters.    The 


384: 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


broad  leaves  of  avocado  trees  are  not  resistant  to  excessive  dry  heat 
as  are  those  of  the  loquat  and  olive  and  are  often  seriously  injured 
by  hot,  dry  winds.  The  trunks  of  young  trees  should  be  shaded  by 
some  form  of  tree  protector  or  by  loosely  wrapped  newspapers,  as 
many  young  trees  have  been  ruined  by  direct  exposure  to  the  mid-day 
sun.  The  branches  are  rather  brittle  and  young  trees  should  be  pro- 
tected  from  violent   winds.     Although   bearing  trees   have  sufficient 


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Fig.  2. — Avocado  flowers  are  perfect  and  usually  set  fruit  in  abund- 
ance. Heavy  rains  at  the  time  of  blossoming  prevent  pollination;  severe 
frosts  may  destroy  the  blossoms  entirely. 


elasticity  to  enable  the  branches  to  carry  heavy  loads  of  fruit  without 
breaking,  it  is  advisable  to  select,  for  planting,  locations  where  the 
wind  is  not  too  severe. 

The  southern  coast  districts  of  California  appear  to  be  well  adapted 
to  avocados  since  many  large  trees  of  various  types  have  been  fruiting 
successfully  there  for  several  years.  Other  parts  of  the  state  from 
Riverside  to  Butte  County  are  now  being  tested  by  planting,  not  only 
seedlings  but,  also,  budded  trees  of  numerous  varieties,  and  some  seem 


Bulletin  254  THE  AVOCADO  IN  CALIFORNIA  385 

to  be  withstanding  successfully  both  the  winter 's  cold  and  the  summer 's 
heat.  It  is  impossible  at  present  to  state  definitely  what  the  geo- 
graphical limits  of  commercial  avocado  culture  will  be.  It  is  not 
unlikely,  however,  that  some  varieties  of  avocados  can  be  grown  suc- 
cessfully wherever  the  orange,  lemon,  and  pomelo  thrive.  Those  who 
contemplate  planting  avocados  in  untried  localities  should  proceed 
cautiously  and  not  plant  any  variety  extensively  unless  they  are 
willing  to  assume  the  risks  of  the  pioneer. 


PROPAGATION  AND  CULTURE 

Avocados  are  easly  grown  from  seed,  but  the  resulting  plants  are 
exceedingly  variable  in  growth,  age  of  bearing,  and  productiveness. 
Some  trees  never  blossom,  others  blossom  but  set  very  little  if  any 
fruit,  while  a  few  produce  very  good  fruit.  Budded  trees  are  repro- 
ductions of  the  tree  from  which  the  bud  was  taken  and  only  budded 
trees  of  known  varieties  should  be  planted  for  commercial  purposes. 
Seedlings  grown  from  the  small,  thin-skinned  Mexican  fruits  are  pre- 
ferred as  stock  for  budding  on  account  of  their  greater  hardiness, 
but  there  are  very  little  if  any  data  at  present  to  show  the  superiority 
of  one  stock  over  another  so  far  as  the  resulting  tree  is  concerned. 

Producing  Seedlings. — Seeds  are  commonly  planted  with  the  point- 
ed end  up,  in  four  or  five-inch  pots  containing  sandy  soil  about  one- 
fourth  of  the  seed  being  left  exposed.  Germination  often  takes  place 
in  one  month  if  bottom  heat  is  used;  in  a  lath  house  or  in  the  open 
three  or  four  months  are  required  for  germination.  In  some  nurseries 
the  seeds  are  germinated  in  seed  beds  and  then  placed  for  a  short 
time  in  four-inch  pots.  Seedlings  should  not  be  left  in  small  pots 
for  any  great  length  of  time.  If  the  root  system  once  becomes  pot- 
bound  or  establishes  a  circular  growth  of  roots,  it  is  very  difficult  to 
get  young  trees  to  thrive  when  planted  out.  When  the  seedlings  are 
from  six  to  eight  inches  high  they  are  transplanted  to  nursery  rows, 
being  placed  about  sixteen  inches  apart  in  the  row.  The  seedlings 
should  be  ready  to  bud  by  the  following  October  or  November,  the 
buds  remaining  dormant  until  early  spring. 

Methods  of  budding. — The  method  of  budding  is  very  similiar  to 
that  used  with  citrus  trees,  a  large  shield  bud  being  preferred.  The 
degree  of  success  in  budding  depends  upon  the  condition  of  the  stock, 
the  selection  of  good  buds,  the  skill  of  the  operator,  and  the  subsequent 
treatment  of  the  plants.  The  following  method  of  budding  has  been 
most  successful.     Select  young  wood  of  the  current  season's  growth, 


386 


UNIVERSITY  OF  CALIFORNIA— EXPERIMENT  STATION 


Bulletin  254  THE  AVOCADO  IN  CALIFORNIA  387 

cut  the  bud  from  one  to  one  and  one-half  inches  long,  insert  it  into  a 
T-shaped  incision  in  the  bark  of  the  stock  whenever  the  sap  is  flowing 
freely,  and  bind  firmly  with  waxed  tape.  At  the  end  of  two  weeks, 
examine  the  work  and  loosen  the  tape  if  it  is  beginning  to  bind  the 
stock  too  tightly.  Remove  the  tape  entirely  at  the  end  of  six  weeks. 
at  which  time  the  bud  should  be  firmly  united  with  the  stock.  The 
bud  is  usually  forced  into  growth  by  gradually  cutting  back,  first, 
the  side  branches  and  later,  the  main  stem  of  the  stock,  the  stub  of 
which  should  not  be  cut  back  to  the  bud  until  the  lower  leaves  of  the 
new  shoot  have  become  quite  mature.  Budded  trees  are  allowed  to 
grow  for  one  }7ear  in  the  nursery  row  before  transplanting. 

Transplanting  from  Nursery. — The  transplanting  of  balled  trees 
from  nursery  rows  is  best  done  from  January  to  March,  and  it  is 
advisable  to  hold  the  trees  in  a  lath  house  for  a  couple  of  weeks  before 
planting.  As  a  result  of  early  planting,  the  trees  will  become  estab- 
lished and  the  new  growth  become  more  or  less  mature  before  the 
heat  of  summer.  Trees  in  orchard  form  should  be  spaced  at  least 
twenty-five  feet  apart.  Young  trees  require  little  pruning  except 
an  occasional  pinching  back  of  vigorous  shoots  to  induce  a  more  sym- 
metrical growth. 

General  Care  of  Trees. — Budded  trees  are  usually  more  or  less 
dwarfed  and  come  into  bearing  early  as  a  rule,  although  there  is 
considerable  variation  among  the  different  varieties  in  this  respect. 
Budded  trees  should  begin  to  bear  profitably  the  fourth  or  fifth  year 
in  the  orchard ;  some  will  begin  fruiting  even  in  the  nursery  row. 
The  avocado  tree  should  be  planted  in  soil  which  has  considerable  depth, 
contains  an  abundance  of  plant-food,  and  is  well  drained.  For  ease 
of  cultivation  and  irrigation,  a  sandy  loam  is  preferable,  but  the  tree 
grows  just  as  well,  if  not  better,  on  a  rather  heavy  soil  with  plenty  of 
humus.  Very  little  if  any  fertilizer  should  be  necessary  until  the 
trees  come  into  bearing;  a  mulch  of  straw  or  coarse  manure  may  be 
placed  around  the  tree  to  conserve  moisture,  but  care  should  be  taken 
to  keep  the  latter  from  direct  contact  with  the  trunk  or  injury  from 
heating  will  occur.  Water  in  abundance  should  be  provided  during 
the  first  season  or  two  in  order  to  keep  the  tree  in  active  growth,  but 
the  amount  should  be  reduced  in  the  late  fall,  as  previously  stated, 
to  induce  the  tree  to  stop  growth  and  mature  its  new  wood  in  prepara- 
tion for  winter.  However,  when  very  hot  days  occur  in  late  summer 
or  fall,  water  should  always  be  given,  if  only  a  bucketful  at  a  time  to 
each  young  tree.  Avocados  require  about  the  same  amount  of  irrigation 
water  as  lemon  trees. 


388 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


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Bulletin  254  THE  AVoCADO  IN  CALIFORNIA  389 

It  is  often  desirable  to  top-work  large  seedlings  or  trees  of  one 
variety  to  another.  This  has  been  successfully  accomplished  by  bud- 
ding into  new  wood  forced  out  for  the  purpose.  The  trees  are  cut 
back  severely  in  the  spring  and  the  ends  of  the  stubs  are  covered  with 
heavy  grafting  wax  or  asphaltum  paint  to  prevent  decay.  Only  three 
or  four  of  the  new  shoots  should  be  left,  and  when  these  have  reached 
a  diameter  of  three-fourths  of  an  inch  they  may  be  budded  in  the 
same  manner  as  seedlings.  The  shoots  from  the  buds  grow  rapidly 
and  often  begin  to  bear  in  two  years. 

PEODUCTION  AND  MARKETING 

Avocado  trees  are  in  many  cases  remarkably  prolific.  Individual 
trees  of  the  thin-skinned  Mexican  type  in  Los  Angeles  County  have 
produced  annually  as  many  as  5000  small  fruits  with  thin  flesh  and 
rather  large  seed.  Such  fruits  are  at  present  valuable  for  their  seeds, 
on  account  of  the  scarcity  of  root  stocks  for  budding.  Many  trees 
fifteen  to  twenty  years  old,  both  of  the  thin-skinned  and  hard-shelled 
types,  have  produced  over  1000  fruits  each  in  one  season,  while  a  few 
have  produced  from  2000  to  2500.  It  is  doubtful  if  such  large  yields 
can  be  obtained  from  orchard  trees  season  after  season,  since  budded 
trees  do  not  usually  grow  as  large  as  seedlings.  A  yearly  average  of 
500  marketable  fruits  per  tree  from  ten  to  fifteen-year-old  trees  planted 
twenty-five  feet  apart  may  be  considered  a  fair  yield.  Some  varieties 
with  small-sized  fruit  may  produce  more. 

The  thin-skinned  avocados  bloom  in  the  late  winter  and  early 
spring,  the  fruit  maturing  from  August  to  December.  The  hard-shelled 
varieties  thus  far  grown  in  California  bloom  early  in  spring  and 
usually  require  more  than  a  year  to  mature.  The  fruit  should  be 
picked  when  mature  and  ripened  off  the  tree,  the  length  of  time  the 
fruit  will  keep  varying  with  the  different  varieties  but  depending 
largely  upon  the  degree  of  ripeness  when  it  is  picked.  If  the  fruit 
is  kept  too  long,  on  retail  fruit  stands,  for  example,  the  oil  in  the 
flesh  becomes  rancid,  rendering  the  fruit  unfit  for  consumption.  Ex- 
periments with  cold  storage  for  avocados  show  that  the  fruit  can  be 
held  at  a  temperature  ranging  from  32°  to  35°  F.  for  a  period  of 
at  least  two  months. 

Avocados  grown  in  California  and  shipped  to  Eastern  or  even 
to  Middle  Western  markets  will  have  to  compete  more  or  less  with 
fruit  from  Florida  and  the  "West  Indies,  especially  in  the  fall  of  the 
year.  Whether  this  competition  can  be  met  with  avocados  as  success- 
fully as  it  is  being  met  with  citrus  fruits  remains  to  be  seen.  Even 
should  it  be  found  impracticable  to  pack  and  ship  thin-skinned  fruits 


390 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


to  Eastern  markets  and  have  them  arrive  in  condition  to  sell  in  com- 
petition with  hard-shelled  fruits  from  Florida,  such  fruit  should  be 
in  demand  in  the  local  markets  for  some  years  to  come. 

Estimates  of  profits  to  be  derived  from  an  avocado  orchard  should 
not  be  based  on  the  performances  of  large  seedling  trees,  nor  on  the 
prices  received  for  fruit  in  the  past.  The  present  price  of  from  $4 
to  $8  a  dozen  may  not  long  be  maintained  when  orchards  now  planted 
come  into  bearing  and  the  fruit  becomes  more  common,  although  high 
prices  will  probably  be  received  for  some  years  to  come.     In  the 


Fig.  5. — The  Solano  is  a  large,  green-fruited  avocado  having  a  small 
seed  and  a  large  amount  of  flesh  of  fair  quality.  Size  of  fruit,  5%  by 
Z7/s  inches. 

United  States  the  avocado  is  a  comparatively  new  and  little  known 
fruit  and  experience  in  San  Francisco  has  shown  that  it  is  easy  to 
overstock  that  market. 

INSECTS  AND  DISEASES 
There  are  no  serious  pests  of  the  avocado  in  California,  although 
in  other  countries  the  tree  and  fruit  are  subject  to  the  attacks  of 
several  injurious  insects  and  fungi.  Shipments  of  avocado  fruit  into 
this  state  from  Hawaii  are  prohibited  on  account  of  the  danger  of 
introducing  the  Mediterranean  fruit  fly  in  the  fruit.  Shipments  from 
Mexico  are  no  longer  made,  since  the  seeds  of  Mexican  avocados  are 


Bulletin  254 


THE  AVOCADO  IN  CALIFORNIA 


391 


liable  to  be  infested  with  the  larva  of  a  weevil  which  might  become 
established  here.  Occasional  shipments  of  one  to  two  hundred  crates 
are  being-made  into  California  from  the  Island  of  Tahiti,  where  the 
fruit  fly  has  not  so  far  been  found,  and  from  Florida,  where  there 
are  no  known  pests  liable  to  be  introduced  with  the  fruit. 

The  fruits  of  some  varieties  of  thin-skinned  avocados  in  California 
have  a  tendency  to  ripen  and  turn  dark  at  the  apex  first  if  left  on 
the  tree  too  long.     In  the  past  this  has  been  considered  to  be  due  to 


Fig.  6. — The  Chappelow  is  a  good  example  of  the  purplish-black,  thin- 
skinned  type  of  avocado.  The  quality  and  flavor  of  such  fruits  is  usually 
very  good.  This  variety  analyzed  29.10  per  cent  of  fat  in  the  fresh  fruit. 
Size  of  fruit,  3%  to  4^  inches  long. 

a  fungus  disease,  and  while  its  exact  nature  is  uncertain  it  has  been 
found  that  this  softening  can  be  largely  avoided,  by  picking  the  fruit 
at  the  proper  stage  of  maturity. 


VARIETIES 

Probably  the  most  important  and  at  the  same  time  the  most 
perplexing  question  confronting  avocado  planters  today  is  that  of 
varieties.  At  least  twenty-five  varieties  of  California  origin  have 
already  been  described  and  doubtless  as  many  more  are  being  propa- 


392  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

gated  and  heralded  by  enthusiastic  owners  or  nurserymen.  In  addi- 
tion, a  score  or  more  varieties  from  other  countries  have  been  intro- 
duced and  are  being  propagated  by  the  thousand  in  some  cases.  The 
unbiased  opinion  of  some  persons  who  have  traveled  in  Mexico  and 
other  countries  and  eaten  avocados  from  native  trees  is  that  the  com- 
mercial avocado  variety  of  the  future  has  not  yet  appeared;  others 
claim  that  some  California  varieties  have  no  superior  anywhere.  New 
kinds  should  be  thoroughly  tested  in  order  to  show  their  adaptability 
to  our  climatic  conditions  before  being  planted  extensively.  California 
seedlings  which  have  been  fruiting  for  several  years  have  a  decided 
advantage,  as  it  is  already  known  what  they  will  do  under  certain 
California  conditions. 

The  requirements  of  a  good  commercial  variety  may  be  briefly 
outlined  as  follows : 

1.  The  bud  of  such  a  variety  should  be  able  to  grow  into  a  vigorous, 
upright,  orchard  tree. 

2.  It  should  be  sufficiently  hardy  to  withstand  ordinary  frosts. 

3.  It  should  be  precocious,  prolific,  and  a  regular  bearer. 

4.  It  should  blossom  late  enough  for  the  flowers  to  escape  heavy 
spring  frosts. 

5.  The  fruit  should  be  of  good  flavor  and  quality. 

6.  The  size  and  shape  of  the  fruit  should  be  uniform  and  not  too 
large,  approaching  oval  or  round,  rather  than  "bottle-necked,"  and 
averaging  about  one  pound  in  weight. 

7.  The  fruit  should  be  well  adapted  to  shipping. 

8.  The  seed  should  be  small  and  tight  in  the  cavity. 

Many  of  the  thin-skinned  Mexican  avocados  are  superior  so  far 
as  flavor  is  concerned  and  are  excellent  fruits  for  home  use  and  local 
market.  Seedlings  and  budded  trees  of  such  varieties  as  the  Harman, 
Northrup,  Chappelow,  and  Carton  grow  vigorously  and  develop  into 
shapely  orchard  trees.  Growers  who  are  undecided  as  to  the  variety 
to  set  out  are  advised  to  plant  a  hardy  type,  such  as  one  of  the  above, 
and,  if  desired,  bud  the  trees  over  a  few  years  hence  when  there  are 
more  reliable  data  regarding  commercial  varieties. 

Pomological  descriptions  of  varieties  are  reserved  for  a  later  publi- 
cation. The  notes  presented  herewith  are  intended  merely  to  assist 
the  grower  in  selecting  the  variety  best  suited  to  his  needs  and  location. 

Thin-Skinned  Varieties : 

Harman. — Purplish  green,  averaging  about  one-half  pound  in  weight,  with 
a  tendency  to  crack  around  the  apex  when  mature;  seed  usually  loose  in  the 
cavity;  tree  hardy,  prolific;  one  of  the  best  of  its  type. 


Bulletin  254 


THE  AVOCADO  IN  CALIFORNIA 


393 


Northrup. — Almost  black,  of  medium  size  and  good  quality;  has  two  crops  a 
year,  a  large  fall  crop  and  a  small  spring  crop. 

Carton. — Very  dark  purple,  pear-shaped,  averaging  about  12  ounces  in  weight; 
surface  smooth,  not  glossy;  quality  good. 

Chappelow. — Black  with  a  glossy  surface,  bottle-necked;  tree  only  moder- 
ately productive;  blossoms  early  and  the  flowers  are  sometimes  injured  by  frost. 

Ganter. — Green,  medium  sized,  of  good  quality;  turns  black  at  the  apex  and 
decays  rather  quickly  when  mature;  tree  hardy,  vigorous,  and  very  productive. 


Fig.  7. — The  seed  of  an  avocado  should  be  small  and  tight  in  the  cavity. 
The  Sharpless,  shown  here,  has  an  exceptionally  large  proportion  of  edible 
matter  and  a  relatively  small  seed.     Size  of  fruit,  6*4  by  3%  inches. 

White. — Black,  elongated,  of  medium  size  and  fair  quality;  surface  smooth 
and  glossy;  has  no  points  to  recommend  it  over  other  varieties. 

The  Fowler  and  Blake  are  green-fruited  varieties,  pear-shaped  and  of  fairly 
good  quality,  but  have  no  strong  characteristics  in  their  favor. 

The  Taft  Hardy,  a  variety  put  on  the  market  last  season,  should  not  be 
confused  with  the  original  Taft,  a  larger,  hard-shelled  fruit. 


Hard-Shelled  Varieties  : 

Taft. — Pear-shaped,  of  over  one  pound  weight,  and  of  extra  good  quality: 
budded  trees  have  not  shown  a  tendency  to  bear  early;  the  original  tree  bears 
regularly  and  is  becoming  more  productive  as  it  grows  older;  tree  ornamental; 
one  of  the  hardiest  of  its  type;  a  leading  commercial  variety. 


394  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

Challenge. — Very  prolific,  bearing  round  fruits  averaging  about  one  pound 
in  weight;  a  very  promising  commercial  variety. 

Lyon. — Large,  pear-shaped,  of  good  quality;  tree  prolific  and  precocious. 

Meserve. — Dark  green,  round,  of  good  size  and  quality;  a  promising  com- 
mercial variety. 

Dickey. — Green,  pear-shaped,  of  good  quality;  difficult  of  propagation;  buds 
start  to  grow  but  seldom  live  more  than  a  few  months. 

Blakeman. — Green,  pear-shaped,  medium  to  large,  of  about  one  pound  weight, 
of  extra  good  quality;  a  promising  commercial  variety. 

Walker. — Pear-shaped,  medium  in  size,  only  fair  in  quality,  its  chief  recom- 
mendations being  precocit}'  and  productiveness. 

Royal. — Oval,  medium  sized,  weighing  one  pound  or  more,  of  fair  quality; 
tree  vigorous,  only  moderately  prolific. 

Miller. — Oval,  of  medium  size  and  fairly  good  quality;  tree  only  moderately 
prolific. 

Nurrietta. — A  good  round-fruited  variety  which  matures  in  the  spring;  a 
desirable  type  and  of  extra  good  quality;  almost  impossible  to  get  buds  to 
develop  into  good  orchard  trees. 

Solano. — Large,  weighs  from  one  to  two  pounds;  quality  good;  tree  productive 
considering  the  size  of  the  fruit. 

Colorado  (commonly  known  as  Purple  Murrietta). — Purplish-black,  rather  large; 
weight  about  one  pound;  flavor  and  quality  good. 

El  Presidente. — Oblong,  pear-shaped,  olive-green,  of  about  one  pound  weight 
and  of  fairly  good  quality. 

Dickinson. — Medium  sized,  dark  purple,  with  very  rough  surface;  tree  vig- 
orous but  rather  tender. 

Sharpless. — Large,  pear-shaped,  averaging  over  one  pound  in  weight;  seed 
very  small  in  proportion  to  amount  of  flesh;  a  promising  variety. 

The  Rhoad,  Senor,  Champion,  Rita,  Ultimate,  and  Beauty  are  varieties  devel- 
oped in  Orange  County  and  are  more  or  less  promising,  but  have  not  been  largely 
propagated. 

The  Wagner  bears  round  fruit  of  medium  size.  The  tree  shows  promise  of 
being  quite  prolific. 

The  Ideal,  Two-pound  Green,  San  Sebastian,  Queretaro,  Redondo,  California 
Trapp,  Montezuma,  Atlixco,  Sinaloa,  Modesto,  Furnival  No.  1,  Popocatepetl, 
Val  de  Flor,  Itzia,  and  Johnson  No.  5  and  No.  6  have  been  introduced  from  the 
highlands  of  Mexico  during  the  last  few  years  and  are  now  under  trial. 

The  Chili  was  introduced  from  the  highlands  of  Chili.  Other  introductions 
have  been  made  from  Guatemala  and  Colombia  and  are  now  being  propagated. 
Among  these  numerous  introductions  there  are  undoubtedly  some  very  hardy 
and  superior  varieties,  but  until  they  have  shown  their  adaptation  to  our  condi- 
tions extensive  plantings  are  not  advisable. 


THE  NUTRITIVE  VALUE  OF  THE  AVOCADO 


BY 
M.  E.  JAFFA 


The  investigation  here  reported  includes  the  analyses  of  28  dif- 
ferent varieties  of  the  avocado.  These  data  emphasize  the  value  of 
this  fruit  as  an  excellent  source  of  easily  digested  vegetable  fat. 

Composition  of  Fruits. — A  reference  to  the  composition  of  fresh 
fruits  in  general  shows  that  the  amount  of  water  is  large  and  that 
the  percentages  of  the  nutrients  indicate  that  the  main  food  value  is 
derived  from  carbohydrates.  In  nearly  all  cases  the  sugars  predomi- 
nate, starch  being  present  in  small  amounts  only. 

The  protein  content  of  fruits  is  low,  varying  from  .2  per  cent  as 
an  average  for  the  loquat  to  2.5  per  cent  for  the  olive.  The  stone- 
fruits  contain,  on  the  average,  less  than  1  per  cent. 

The  figures  for  the  mineral  matter  or  ash  in  fresh  fruits  are,  in 
general,  much  lower  than  the  corresponding  data  for  meats  or  grain. 
The  average  for  meat  is  about  1  per  cent,  while  for  fruit  it  is  much  less. 

It  must  not  be  forgotten,  however,  that  while  the  amount  of  ash  is 
small,  the  percentage  of  potassium,  so  essential  to  the  animal  economy, 
is  high.  This  is  a  very  valuable  base-forming  element  which  is  neces- 
sary in  the  maintenance  of  the  normal  neutrality  of  the  blood  and 
tissues.  The  importance  of  the  mineral  matter  in  nutrition  and  the 
necessity  of  carefully  selecting  the  dietary  so  as  to  secure  a  proper 
balance  between  the  base-forming  and  acid-forming  elements  is  be- 
coming more  and  more  apparent. 

Fat  is  present  in  very  small  proportions  in  fresh  fruits.  This 
constituent  is  generally  reported  as  "Ether  Extract,'  which  often 
contains  other  materials  than  true  fat  or  oils,  such  as  coloring  matter, 
wax  found  in  skin,  etc.  The  figure,  therefore,  reported  for  fat  in  most 
fruits  is  seldom  a  true  indication  of  the  content  of  this  nutrient. 

COMPOSITION  OF  THE  AVOCADO 

A  survey  of  the  data  presented  shows  the  avocado  to  differ  widely 
in  many  respects  from  the  average  of  fresh  fruits  and  proves  it  worthy 
of  special  consideration.  It  might  almost  be  said  to  be  in  a  class  by 
itself. 

[395] 


396 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


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THE  AVOCADO  IN  CALIFORNIA 


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398 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


The  tables  are  replete  with  interesting  points,  all  very  favorable 
to  the  avocado.  The  total  dry  matter  in  the  edible  portion  is,  in 
nearly  every  instance,  greater  than  that  noted  for  any  fresh  fruits. 
The  average  for  the  avocado  is  30.84  per  cent.  The  nearest  approach 
to  this  figure  is  found  in  the  banana,  with  about  25  per  cent  dry 
matter.  It  must  be  remembered,  however,  that  while  there  may  not 
be  so  much  difference  in  the  total  solids  of  the  two  fruits  in  question, 
there  is  a  great  difference  in  the  nature  of  the  nutrients.  Sugar  and 
starch  predominate  in  the  banana  as  against  fat  in  the  avocado. 


Fig.  8. — The  Challenge  has  a  thick,  hard  shell;  rough,  shiny  surface, 
rather  large  seed,  and  fair  quality  of  flesh.  The  original  tree  is  produc- 
tive, about  2500  fruits  having  been  picked  in  1915.  Size  of  fruit,  3i/>  by 
3%  inches. 

It  has  been  stated  that  the  protein  per  cent  in  all  fruits  is  low 
averaging  less  than  1  per  cent.  It  will  be  seen  from  the  table  that 
the  minimum  figure  for  protein,  1.30  per  cent,  is  nearly  equal  to  the 
maximum  indicated  for  fresh  fruit,  1.5  per  cent,  noted  for  figs  and 
currants.  The  maximum,  3.7  per  cent,  corresponds  somewhat  closely 
to  the  protein  content  of  some  dried  fruits.  In  three  varieties  the 
protein  is  present  in  excess  of  3  per  cent ;  in  ten  varieties  considerably 
above  2  per  cent ;  while  the  average  for  the  28  varieties  is  2.08  per  cent. 
It,  therefore,  may  be  said  that  so  far  as  protein  in  fresh  fruits  is 
concerned,  the  avocado  stands  far  in  the  lead. 

The  carbohydrate  content  of  the  avocado,  with  the  exception  of 
seedlings  Nos.  5  and  6  submitted  by  O.  M.  Cadwell  of  Carpinteria, 
is  low  as  compared  with  this  constituent  in  fresh  fruit.  The  average 
for  the  28  varieties  is  7.39  per  cent,  and  this  would  have  been  appreci- 


Bulletin  254 


THE  AVOCADO  IN  CALIFORNIA 


399 


ably  lowered  if  the  data  for  the  two  seedlings  above  mentioned  had 
been  omitted  from  the  average. 

The  figures  quoted  in  the  table  for  carbohydrate  include  crude 
fiber,  which  was  not  determined  in  every  case.  Analyses  have  shown, 
however,  that  this  ingredient  is  present  to  the  extent  of  about  1.75 
per  cent,  comparing  favorably  with  the  content  of  fiber  in  the  other 
fresh  fruits. 

It  is  of  decided  interest  to  note  that  the  mineral  matter  in  the 
avocado  is  much  greater  than  that  found  in  any  fresh  fruit.  Just 
how  much  importance  can  be  attached  to  this  fact  can  better  be  stated 


Fig.  9. — The  Ganter  is  a  green-fruited  variety  having  a  thin  skin  and 
good  quality  of  flesh.  The  rattling  of  the  loose  seed  in  the  cavity  with 
the  consequent  bruising  of  the  flesh  is  a  slight  disadvantage  in  marketing. 


after  the  conclusion  of  the  detailed  analysis  of  the  ash,  which  will 
indicate  the  per  cent  of  potassium,  calcium,  phosphoric  acid,  iron,  etc. 
The  results  of  the  ash  analyses  will  be  published  as  a  supplementary 
report. 

The  minimum  per  cent  of  ash,  .60,  noted  for  the  variety,  Cardinal, 
from  Florida,  exceeds  the  per  cent  of  ash  determined  for  apples,  apri- 
cots, grapes,  blackberries,  oranges,  pears,  and  plums,  and  fully  equals 
the  corresponding  figure  for  cherries,  figs,  melons,  and  prunes. 

The  minimum  per  cent  of  ash  noted  for  a  variety  grown  in  Cali- 
fornia is  0.80  per  cent,  exceeding  that  found  in  any  of  the  fresh  fruits. 
As  seen  from  the  table,  the  average  for  the  28  varieties  is  1.26  per  cent, 
only  slightly  below  the  ash  percentage  in  dates. 


400 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


The  foregoing  discussion  clearly  indicates  that  so  far  as  protein 
and  ash  in  fresh  fruits  are  concerned,  the  avocado  stands  at  the  head 
of  the  list,  and,  with  reference  to  the  carbohydrates,  contains  on  an 
average  fully  50  per  cent  of  that  found  in  many  fresh  fruits.  These 
facts  alone  would  warrant  due  consideration  being  given  to  the  value 
of  the  avocado  as  a  fresh  fruit. 

The  chief  value  of  the  avocado  as  food,  however,  is  due  to  its  high 
content  of  fat.  This  varies,  as  shown  by  the  analyses,  from  a  minimum 
of  9.8  per  cent  to  a  maximum  of  29.1  per  cent,  with  an  average  of 
20.1  per  cent. 

Reviewing  the  analytical  data,  it  will  be  seen  that  ten  varieties 
show  more  than  23  per  cent  fat  and  seven  other  varieties  an  excess 
of  18  per  cent. 

The  only  fruit  comparable  with  the  avocado  in  this  respect  is  the 
olive.  In  this  connection,  it  is  of  interest  to  compare,  as  shown  in  the 
following  table,  the  fat  percentages  of  the  edible  portion  of  those  ten 
varieties  of  the  avocado  containing  23  per  cent,  or  upwards,  of  fat 
with  ten  varieties  of  the  olive. 


Table  2. — Showing  Percentage  of  Fat  or  Oil  in  the  Avocado  and  Olive 


Avocado 

A 

Olive 

A 

r 

Original  mat 
Edibl* 

erial  water  free 
i  portion 

A 

Fat, 
per  ct. 

78.01 
74.67 

70.88 

r 

Original  material 
Edible  portion 

Variety 
Corregiolo 
Nigerina 
Nevadillo  Blanco 

-* 

r 

No.  and  Variety 
8.  Chappelow 

15.  Seedling  No. 

14.  Northrup 

1 

Water, 
per  ct. 

60.94 
62.65 
61.08 

Fat, 
per  ct. 

29.10 
27.89 
27.60 

Oil, 

per  ct. 

27.68 
26.16 
22.92 

13. 

Mattern 

61.55 

25.70 

66.84 

Mission 

22.51 

1. 

Ganter 

63.86 

25.60 

70.84 

Rubra 

22.01 

7. 

Blake 

67.40 

25.50 

74.48 

Pendulina 

21.36 

3. 

Miller 

66.60 

23.70 

70.96 

Redding  Picholine 

20.83 

17. 
11. 

Seedling  No. 
Unnamed 

3 

65.10 
65.50 

23.40 
23.10 

67.05 
66.96 

Maerocarpa 
Manzanillo 

20.41 
19.73 

26. 

Northrup 

66.31 

23.00 

68.27 

Columbella 

19.54 

.  !  J  :  j  .  •  \i  .  . .  if  L;  t  i  !  '  I  i-oi  .i  «J  ■*:«,  I ■•■?*-.  ijam  .  :■:  _l_U.Li_i  ^Li^imLujttJji 
The  figures  in  Table  2  indicate  that  the  avocado  ranks  higher  in 
fat  or  oil  than  the  average  or  commonly  used  olive.  The  latter  fruit 
also  has  the  disadvantage  of  requiring  special  treatment  before  it  is 
ready  for  consumption  and  should  really  rank  as  a  processed  fruit 
rather  than  a  fresh  one.  The  data  in  the  table  show  that  when  consid- 
ering the  dry  matter  only  No.  8,  Chappelow,  shows  the  highest  per- 
centage of  fat.  In  the  original  conditions  the  Northrup  and  an  un- 
named fruit  differ  by  nearly  4  per  cent,  which  difference  is  practi- 
cally eliminated  when  comparison  is  made  on  a  water-free  basis,  which 
is  the  only  true  way  to  compare  the  nutritive  value  of  fruits. 


Bulletin  254 


THE  AVOCADO  IN  CALIFORNIA 


401 


CALORIC  VALUE 

While  it  is  true  that  the  real  value  of  any  food  is  not  always 
represented  by  the  heat  units  or  calories,  at  the  same  time  the  total 
food  value  is  so  indicated.  This  difference  between  the  real  value  and 
total  food  value  is  not  always  properly  understood.  For  instance,  the 
energy  value  of  a  pound  of  sugar  is  1820  calories,  while  the  corre- 
sponding value  for  lean  meat  is  less  than  1000  calories.  Yet  we  would 
hardly  say  that  the  real  value  of  a  pound  of  sugar  was  1.8  times  that 
of  a  pound  of  lean  meat,  if  the  question  of  growth  were  under  consid- 
eration. When,  however,  the  matter  of  energy  is  being  discussed  the 
case  is  entirely  different,  and  the  value  of  a  food  as  a  source  of  energy 
varies  directly  with  its  caloric  value. 

The  energy  values  of  the  edible  portion  of  the  commonly  used 
fresh  fruits  are  low,  ranging  from  a  minimum  of  175  calories  to  a 
possible  maximum  of  400  calories  per  pound. 

An  inspection  of  Table  3  shows  that  the  avocado  has  a  far  higher 
value  in  this  respect ;  the  average  of  twenty-six  varieties  being  984 
calories  per  pound,  or  more  than  twice  the  maximum  noted  for  other 
fruits.  The  minimum  figure,  597,  is  also  in  excess  of  this  maximum. 
The  maximum,  1325  calories  per  pound,  approaches  that  noted  for 
some  varieties  of  dried  fruits.  It  corresponds  to  about  75  per  cent 
of  the  fuel  value  of  the  cereals  and  is  not  far  from  twice  that  noted 
for  average  lean  meat. 


Table  3. — Showing  the  Energy  Value  of  the  Avocado 


No. 
1. 

and  Variety 
Ganter 

Energy  value 

per  lb. 

Calories 

1194 

No. 
15. 

and  Variety 
Seedling 

No. 

1 

Energy  value 

per  lb. 

Calories 

1282 

2. 

Harman 

923 

16. 

Seedling 

No. 

2 

812 

3. 

Miller 

1107 

17. 

Seedling 

No. 

3 

1132 

4. 

Walker 

952 

18. 

Seedling 

No. 

4 

]019 

5. 

Sharpless 

741 

19. 

Seedling 

No. 

5 

846 

6. 

Chappelow 

1325 

20. 

Seedling 

No. 

6 

948 

7. 

Blake 

1147 

21. 

Harman 

852 

8. 

Chappelow 

867 

22. 

White 

722 

9. 

Carton 

23. 

Fowler 

987 

10. 

Carton 

949 

24. 

Northrop 

11. 

Unnamed 

1115 

25. 

Cardinals 

597 

12. 

Topa  Topa 

778 

26. 

Northrup 

1]01 

13. 

Mattern 

1240 

27. 

Trapp 

599 

14. 

Northrup 

1303 

28. 

Azusa 

1 042 

402  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

DIGESTIBILITY 

There  have  been  no  metabolism  experiments  carried  on  in  con- 
nection with  the  avocado,  yet  it  is  only  fair  to  assume  that  this  fruit 
is  as  easily  digested  as  many  others  whose  coefficients  have  been  deter- 
mined. Such  data  clearly  prove  that  the  fruits  are  quite  thoroughly 
digested.  While  the  availability  of  the  protein  rates  below,  the  diges- 
tion coefficients  of  the  carbohydrates  compare  favorably  with,  and 
those  of  the  oils  and  mineral  matter  are  fully  equal  to  those  obtained 
for  the  mixed  diet. 

DIETETIC  VALUE 

The  dietetic  value  of  fruit,  aside  from  the  actual  nutrients  which 
it  contains,  lies  in  its  succulency — its  minerals  and  organic  acids.  If 
gauged  by  its  nutritive  value  alone,  fruit  would  seem  to  be  an  ex- 
pensive form  of  nourishment,  but  when  its  hygienic  qualities  are 
considered  its  money  value  to  the  consumer  is  difficult  to  estimate. 
Some  fruits  carry  more  nourishment  with  their  hygienic  properties 
than  others.  Some  contain  minerals  which  are  more  valuable  to  the 
system  or  less  commonly  distributed  than  others.  Therefore,  while 
there  are  general  properties  which  are  common  to  all  fruits,  each  has 
special  properties  which  justify  individual  consideration. 

While  the  special  dietetic  value  of  a  food  can  not  always  be  fore- 
cast by  the  chemical  analysis,  it  is  certainly  permissible  to  suggest  the 
possibilities  which  are  indicated  through  such  investigation.  It  is 
always  necessary  that  such  theory  be  confirmed  by  clinical  experience. 

Judging  from  its  composition,  the  avocado  should  perhaps  prove  to 
have  laxative  qualities  of  a  peculiar  or  individual  type,  possessing  as 
it  does  the  combination  of  the  usual  "fruit  principles,"  and  that  of  fat 
or  oil.  The  laxative  properties  of  most  fruits  depend  upon  the  stim- 
ulating effects  of  the  fiber  upon  the  wall  of  the  intestine  and  partly 
upon  the  organic  acids  and  minerals.  Oil  has  a  tendency  to  soothe  and 
to  lubricate  the  intestine  even  while  it  acts  as  a  mild  laxative.  The 
avocado  is  a  natural  combination  of  these  two  types  of  foods — as  if 
fruit  and  olive  oil  had  been  chemically  combined  by  nature.  Whether 
or  not  there  is  any  special  advantage  in  this  natural  combination  over 
that  made  by  a  proper  selection  of  foods  remains  to  be  proved.  There 
are  no  clinical  data  on  the  subject,  but  future  experimental  work  may 
give  some  interesting  results. 

The  fact  that  the  native  Cubans  prefer  this  fruit  to  any  other  of 
their  abundant  supply  may  be  due  to  its  flavor  alone,  but  it  is  more 
than  likely  that  the  preference  is  more  deep  seated,  and  that  it  is  the 
result  of  generations  of  experience  or  of  a  knowledge  of  its  beneficial 
effects. 


